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Acta Mechanica Sinica
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15 June 2012, Volume 34 Issue 3
Around the mechanics
THE PROGRESS OF STUDIES OF UNCOMMANDED MOTION AND ITS SUPPRESSION OF FLYING VEHICLE WITH HIGH MANUEVERABILITY
DENG Xueying, ZHU Jun, WANG Yankui, MA Baofeng
2012, 34(3): 1-8. doi:
High maneuver ability might be achieved by a flying vehicle at high angles of attack. The uncom-manded motions of aircraft can be generated at high angles of attack in flying with high maneuver ability. Therefore this problem should be considered in the early phase of aircraft design and the complicated flow behaviors and characteristics of uncommanded motions of the designed configuration will be studied to reveal the dominant flows to drive uncommanded motions. The flow control techniques are developed to suppress the uncommanded motions. In the present paper it is pointed out that the forebody asymmetric vortices are very sensitive to the micro-perturbation on the model nose. For a long time it is wrongly believed that the forebody asymmetric vortex flow is non-deterministic. It is found that if a micro-manual-perturbation is added on the nose tip of model the asymmetric vortex flow can be reproduced. Based on the manual-perturbation technique the evolution of the asymmetric vortices related with the circumferential angle of perturbation is revealed. The dominant flows are discovered, which drive the uncommanded motions of two typical configura-tions. The perturbation control techniques are developed to suppress those uncommanded motions by rotating the tip-perturbation and setting tip-perturbation on a proper location to make two pair of asymmetric vortices in the phase reversal. The micro-perturbation plays a very important role in the non-liner separated and vortex flows at high angles of attack. The roles of micro-perturbation are the key in controlling the non-linear vortex flows, which drive the uncmmande motions.
THE CHARACTERISTICS OF DAMAGE CAUSED BY IMPACT ON THE WHIPPLE SHIELD OF LOW-DENSITY BRITTLE MICRO-METEOROID
ZHU Dangdang, PANG Baojun, CHEN Haibo, JIA Bin
2012, 34(3): 9-11,28. doi:
In this paper, numerical impact experiments on spacecraft typical Whipple shield with silicate pro-jectile as low-density brittle micro-meteoroids are carried out to obtain a low-density brittle micro-meteoroids' damage mode and damage law. It is shown that when the projectile impact velocity is between 1.1 km/s and 1.4 km/s, the front plate injury model changes from the petal-type cracking into the hole, when the speed is 1.4 km/s the cracks appear on the drum header. With the increase of the projectile speed, flakes occur on the back plate, and the petal-type crack is formed. When the projectile impact speed is 1.95 km/s, the back plate cracks into the hole, leading to the destruction of protective structures.
APPLICATION OF MESH-LESS METHOD IN ANALYSIS OF ELASTIC-PLASTIC STABILITY OF AN EDGE SLOPE
WEI Demin, HU Yuanzhe, JIANG Xueling
2012, 34(3): 12-17. doi:
The element-free Galerkin method(EFGM) is applied to solve the elastic-viscoplastic problems in this paper. The corresponding computational program is written and applied to the elastic-plastic stability analysis of the edge slope. The comparisons and analyses of the numerical results of EFGM and FEM show that EFGM for elastic-viscoplastic problems is effective with good computational stability and convergence.
MECHANICAL ANALYSIS OF WHOLLY GROUTED ANCHOR IN ROCK SLOPE
GUO Yongjian, SUN Yang
2012, 34(3): 18-22. doi:
Based on the Mindlin's solution of displacement for a concentrated force in space, combined with the well assumed mechanical characteristic form of the wholly grouted anchor in a joint plane, with the sliding force as a concentrated force, the formulas for the axial force and the shearing stress along the anchor are obtained. With them applied to rock slopes, the axial force and the shearing stress along the bolt for rock slopes of rock mass of different types are obtained.
MODELING COMPLICATED STRESS PATH OF CLAYS USING ANISOTROPIC ELASTIC-VISCOPLASTIC MODEL
QIN Yazhou, SU Jianwei, XU Jiancong
2012, 34(3): 23-28. doi:
This paper presents an improved three-dimensional anisotropic elastic-viscoplastic constitutive model based on overstress theory of Perzyna. A rotational hardening law of Wheeler is adopted to account for the initial anisotropy and the changes in anisotropy due to the viscous strains. The developed model is implemented by using ABAQUS software with UMAT subroutine, which is integrated with a return mapping algorithm. The undrained triaxial test for HKMD under complicated loading conditions and the multi-stage undrained triaxial creep test for Sachville clay were simulated by the proposed model. The simulated results show that the proposed anisotropic elastic-viscoplastic model can successfully reproduce the rate-sensitivity, relaxtion, creep and anisotropic behaviors of soft clays under different loading conditions.
THE CRITICAL LOAD OF THE OPEN THIN-WALLED COMPRESS BAR IN CONSIDERATION OF SHEAR LAG EFFECT AND GEOMETRY NONLINEARITY
CHEN Yuji, LUO Qizhi
2012, 34(3): 29-31,35. doi:
Different shear warp displacement functions are assumed for the top flanges and bottom flanges. The energy function for the open thin-walled compress bar is obtained. Based on the minimum potential energy principle, the characteristic equation of the compress bar is derived. The critical load and the correct coefficient for Eular formula of the simple-supported compress bar are calculated. The influence of the width, the thickness of the flange and the span of the compress bar as well as the geometry nonlinearity on the corrent coefficient of the critical load is discussed. The conditions for the applications of Eular critical load formula are discussed.
AN APPLICATION OF RESPONSE SURFACE METHOD TO STRUCTURAL PARAMETER SENSITIVITY AND RELIABILITY ANALYSIS
CHEN Xueqian, XIAO Shifu, LIU Xin'en
2012, 34(3): 32-35. doi:
It is often necessary to study parameter sensitivity and structural reliability. The test design points of input-variables are obtained by the Box-Behnken matrix method in this paper. According to the responses of specimens, the coefficients of the response surface function are identified by a least-squares regression. The steps of calculating probability sensitivity are as follows, firstly, computing the gradients of input-variables respec-tively, secondly, multiplying the gradient and the related range, and finally normalizing the above quantities. The structural reliability is analyzed by combining the response surface model and the first-order second-moment method. The sensitivity and the reliability of an example are analyzed by the response surface method and the Monte Carlo method in ANSYS. The results of two methods are consistent, which shows that the method in the paper is valid and feasible.
CALCULATION OF COMPRESSIVE BEARING CAPACITY OF CONCRETE-FILLED TWIN STEEL TUBES BASED ON TWIN SHEAR UNIFIED STRENGTH THEORY
ZHANG Yufen, ZHAO Junhai, LIU Yiying
2012, 34(3): 36-42. doi:
With consideration of the double confinement to the concrete from the twin tubes, the stresses in the concrete and the steel tubes were analyzed, and the ultimate compressive strength was calculated based on the twin shear unified strength theory. The strength reduction factor (
) was deduced according to plasticity theory, and the confining force between the steel and the concrete was also obtained. Then, the ultimate load capacities of the concrete filled twin steel tubes under axial compression was computed. In comparison with the corresponding experimental results, it is shown that the twin shear unified strength theory can be used in the calculation of the axial capacity. The axial compressive strength of composite column was shown to be influenced by the diameter-to-thickness ratio and the diameter of the inner circular steel tube. The optimal design of the inner steel tubes is presented for the engineering application of these composite columns.
Around the mechanics
ANALYSIS ON STRUCTURE AND THERMAL STABILITY OF GOLD NANOWIRE COVERED ON THE SURFACE OF CARBON NANOTUBE
ZHANG Xingwang, GU Chengjun
2012, 34(3): 43-47. doi:
In this paper, we study the structure and the thermal stability of gold atoms covered on the surface of carbon nanotubes by molecular dynamics simulations. It is shown that, diversiform stable structures can form on the surfaces of carbon nanotubes: when the density of gold atoms covered on the surfaces of carbon nanotubes is less than 15.91, gold atoms would form gold nanoparticles, when the density is between 15.91 and 104.98, gold atoms would form a series of cylindrical and helical shell structures, when the density is greater than 104.98, gold atoms would have the face centered cubic structure like the crystalline bulk gold. Further more, we have also studied the thermal stability of the helical shell nanowires with the carbon nanotubes' support. The results show that the melting point of the helical shell nanowires with the carbon nanotubes' support is lower than the gold nanowires formed in a free space, but higher than that of the gold nanoparticles.
THE EXPERIMENTAL STUDY OF DYNAMIC STRENGTH OF AEOLIAN SOIL IN WEST OF LIAONING PROVINCE
ZHANG Xiangdong, FAN Shixing, LIU Jiashun, ZHANG Jianjun, LAN Changyu
2012, 34(3): 48-52,47. doi:
Dynamic properties and liquefaction characteristics under dynamic loads of Aeolian soil in the west of Liaoning province were studied through dynamic triaxial tests. The dynamic strength of Aeolian soil was determined when the seismic fortification intensity is 7 degree under different test control conditions, including dynamic amplitudes, consolidation ratio and consolidation pressure. The empirical formulas relating dynamic strength to consolidation ratio and consolidation pressure were obtained by the regression analysis of the experimental data by using Excel. Tests and regression analysis results show that dynamic strength of Aeolian soil is proportional to the confining pressure and the consolidation ratio. The soils' liquefaction strength was also studied. Liquefaction shear stress ratios under different consolidation ratios were obtained. Test results show that the liquefaction shear stress ratio is proportional to the consolidation ratio. The test results provide some practical guidance for the projects in west of Liaoning province
APPLICATION OF FLOW FIELD'S PHYSICAL PROPERTIES IN ESTIMATING FLUCTUATING WIND PRESSURE COEFFICIENT
WANG Yingge, LI Zhengnong
2012, 34(3): 53-57,83. doi:
To compute fluctuating wind pressure via numerical simulation technology requires unsteady tran-sient simulation whose computation load is too huge. In order to raise computation efficiency, this paper substituted reference points' wind velocity by that of forecast points' entrance basing on quasi-steady theory, so the estimation formula by Paterson, Huang et al. got revised. The fluctuating wind pressure coefficients of plate structure supported by independent column were estimated according to parameters produced by CFD such as their mean wind pressure coefficient, reference points' wind velocity, onflow's kinetic energy. In most cases, the outcome coincided with the result of wind tunnel test. The research shows that the parameters obtained from steady simulation result could be used to estimate the fluctuating wind pressure coefficient.
ADAPTIVE MESHLESS METHOD AND ITS APPLICATION IN THE CONTACT PROBLEM OF THE BIOACTIVE COATING
ZHANG Zheng, WU Huaping, CHAI Guozhong, BAO Yumei, WU Helong
2012, 34(3): 58-61,42. doi:
The adaptive meshless methods, which have lots of advantages, such as does not need any mesh information, the nodes can be moved, inserted and deleted freely, suitable for adaptive analysis to achieve high computation precision with a less number of nodes and less computation time for a given error tolerance, are convenient for the complex problems which the finite element method can not or is difficult to solve. The theoretical basis and the development direction of the adaptive meshless method are discussed in detail, based on the strain-energy-gradient adaptive meshless algorithm coupling with the finite element method, the contact problem without friction of the two kind plasma spraying bioactive coatings is analyzed, the distribution of the von Mises stress is given. The result shows that the adaptive meshless model can be applied to the contact problem of the biocomposites.
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